Aim: To assess the role of adenosine receptors in the cardioprotective effect of preconditioning and the characterization of adenosine receptors in heart.
Methods: In 18 anesthetized rabbits, myocardial ischemia was induced by occlusion of left descending coronary artery. ST segment elevation in epicardial electrogram was used as a criterion of acute ischemic injury. Myocardial adenosine receptors were measured using [3H] adenosine ligand.
Results: After 60-min ischemia, epicardial ST segment elevation was higher in ischemia group (13.9 +/- 0.6 mV) than in the ischemic preconditioning group (3.1 +/- 0.5 mV). In membranes of the ventricular myocytes prepared from ischemic-preconditioning group, the density of adenosine receptors was higher than that of ischemia and sham ischemia groups (Bmax being 602 +/- 40, 348 +/- 28, and 335 +/- 30 pmol/g protein, respectively). Affinity of the receptors for the [3H] adenosine was not different in the 3 groups (Kd being 181 +/- 18, 169 +/- 21, and 196 +/- 24 nmol . L-1, respectively).
Conclusion: Activation of adenosine receptors along with an increase in adenosine receptor density during ischemic-preconditioning provides the basis for adenosine to exert its protective effect on the ischemic heart.